1. Field of the Invention
This invention relates to a buoyant cable antenna for submarine communication utilizing a flexible polymer composition having a specific gravity sufficient to provide positive buoyancy to the antenna. The invention further relates to a method of making the submarine buoyant cable antenna.
2. Description of the Prior Art
For many years, the U.S. Navy has used a material known as "syntactic foam" to add buoyancy to a number of different devices and underwater vehicles. Syntactic foam is made by mixing glass microballoons into an epoxy matrix. The resulting material is a hard, brittle and lightweight foam that can be cast, but is typically machined, into the final desired shapes. The castings produced in this manner often exhibit density stratifications, a fact which usually results in certain sections of the castings to be cut off and discarded. Contemporary syntactic foams exclusively use a stiff, hard, e.g., epoxy, matrix because it is believed that a rigid matrix is necessary for the foam to survive any significant amount of hydrostatic pressure. This "conventional wisdom" holds that flexible matrices will allow individual microballoons to come into contact with each other under high pressure, and it is feared that such contact will fracture the microballoons and cause the material to lose its buoyancy. These epoxy based matrices being brittle have a tendency to chip or crack.
Additionally, certain foam compositions have been used to provide neutral buoyancy to seismic streamers. A seismic streamer is a linear streaming sonar array towed behind a ship in generally calm subsurface ocean layers. For example, U.S. Pat. Nos. 3,480,907 and 3,900,543 disclose the use of certain foam materials to impart neutral buoyancy to seismic streamers. These foams generally have a specific gravity ranging from 0.72 to 0.85 grams per cubic centimeter.
The prior art does not disclose or suggest a buoyant cable antenna for a submarine using a flexible polymer composition which imparts positive buoyancy to the antenna and which is lightweight and can be bent or coiled without cracking or breaking.
Submarines need to be able to send and receive messages. It has been proposed to maintain radio reception from a submerged submarine through a buoyant cable antenna ("BCA") which rises above the submarine and floats and streams at the ocean surface. When not in use, the BCA is coiled around a small diameter spool in the submarine. The BCA is released to the ocean from a mechanism in the submarine known as a BRA-24. This mechanism exerts substantial force on the BCA when it is released from the submarine to the ocean and returned to the submarine.
The prior art syntactic foams used by the U.S. Navy to provide buoyancy to other devices are not useful in a submarine BCA. Space inside a submarine must be utilized as efficiently as possible. When not in use, the BCA is stored coiled on a spool twelve inches in diameter. The stiff and brittle standard syntactic foams would break is an attempt were made to store a BCA made using them in such a manner. Such a BCA would, in all likelihood, be chipped or otherwise damaged during its passage through the BRA-24 deployment mechanism.
The foams used in the prior art seismic streamers are similarly not useful in a submarine BCA. Seismic streamers trail a floating vessel in generally calm subsurface waters and such conditions differ significantly from a submarine BCA which must rise from the submerged submarine and must be capable of use in all types of sea conditions. Thus, the submarine BCA requires a different and more demanding structure and composition. For example, the submarine BCA is subjected to severe mechanical shocks when towed in high sea conditions, e.g. the BCA must rise from various depths and may be subjected to waves up to 35 feet at the ocean surface. Additionally, the known seismic streamers are made of compositions which provide neutral buoyancy and have a specific gravity in the range of 0.72 to 0.85 grams per cubic centimeter.